It has been demonstrated that CD8+ cytotoxic T lymphocytes (CTLs) recognize epitope peptides derived from tumor-associated antigens (TAAs) presented on MHC class I molecule, and then kill the tumor cells. Since the discovery of the MAGE family as the first example of TAAs, many other TAAs have been discovered using immunological approaches (Boon T, Int J Cancer 54: 177-80, 1993; Boon T et al., J Exp Med 183: 725-9, 1996; van der Bruggen P et al., Science 254: 1643-7, 1991; Brichard V et al., J Exp Med 178: 489-95, 1993; Kawakami Y et al., J Exp Med 180: 347-52, 1994), and some of them have now been in the process of clinical development as targets of immunotherapy.
Identification of new TAAs, which induce potent and specific anti-tumor immune responses, warrants further development of clinical applications of peptide vaccination strategies in various types of cancer (Harris C C, J Natl Cancer Inst 88: 1442-5, 1996; Butterfield L H et al., Cancer Res 59: 3134-42, 1999; Vissers J L M et al., Cancer Res 59: 5554-9, 1999; Van der Burg S H et al., J Immunol 156: 3308-14, 1996; Tanaka F et al., Cancer Res 57: 4465-8, 1997; Fujie T et al., Int J Cancer 80: 169-72, 1999; Kikuchi M et al., Int J Cancer 81: 459-66, 1999; Oiso M et al., Int J Cancer 81: 387-94, 1999).
Various kinds of antigen specific immunotherapy have been performed, however, low clinical efficacy has been obtained so far in terms of obvious tumor regression (Rosenberg S A et al., Nat Med 10:909-15, 2004). One of the major reasons is the poor immune response of tumor-infiltrating lymphocytes (TIL) and peripheral blood lymphocytes (PBL) from patients with advanced-stage cancer (Miescher S et al., J Immunol 136: 1899-907, 1986). This immunosuppression induced by tumor is the reason for poor responses to tumor antigens (Young R C et al., Am J Med 52: 63-8, 1972), poor proliferation of T cells (Alexander J P et al., Cancer Res 53: 1380-7, 1993), loss of cytokine production (Horiguchi S et al., Cancer Res 59: 2950-6, 1999), and defective signal transduction of T cells and natural killer cells (Kono K et al., Clin Cancer Res 11: 1825-8, 1996, Kiessling R et al., Cancer Immunol Immunother 48: 353-62, 1999).
To improve the clinical efficacy for immunotherapy, it is important to overcome the effect of immunosuppressive factors induced by tumors. Immunological tolerance and protection from autoimmunity are conferred by central and peripheral mechanisms including clonal deletion of self-reactive T cells in thymus and the induction of anergy upon encounter with autoantigens in the peripherary. Recently, it has been clarified that regulatory T cells (T-regs), characterized by coexpression of CD4 and CD25 markers, are a functionally unique population of T cells and function to maintain immune homeostasis (Sakaguchi S et al., J Immunol. 155: 1151-64, 1995, Dieckmann D et al., J Exp Med 193: 1303-10, 2001). T-reg cells are one of the major players to suppress the various types of immune response (Miescher S et al., J Immunol 136: 1899-907, 1986; Young R C et al., Am J Med 52: 63-72, 1972; Alexander J P et al., Cancer Res 53: 1380-7, 1997; Horiguchi S et al., Cancer Res 59: 2950-6, 1999; Kono K et al., Clin Cancer Res 11: 1825-8, 1996; Kiessling R et al., Cancer Immunol Immunother 48: 353-62, 1999).
Although the molecular interactions and signaling pathways that are critical for generation and function of T-regs are not yet fully elucidated, T-regs require forkhead transcription factor scurfin (Foxp3; SEQ ID NO 2) encoded by the Foxp3 gene (GenBank Accession No. NM—014009; SEQ ID NO 1), which controls their development and regulatory properties (Fontenot J D et al., Nat Immunol 4: 330-6, 2003, Hori S et al., Science 299: 1057-61, 2003, Khattri R et al., Nat Immunol 4: 304-6, 2003). Further, vaccination of mice with Foxp3 mRNA-transfected dendritic cells elicited a Foxp3-specific CTL response (Smita N et al., Cancer Res. January 1; 67(1):371-80, 2007).
Thus, Foxp3 serves as a target for cancer immunotherapy and furthermore, partial peptides of the protein encoded by Foxp3 serve as antigens recognized by CTL.